The present invention relates to energy efficient windows and, in particular, to a sealed window having a plurality of suspended films and controls to extend and retract the films to control thermal efficiency.
Energy loss through glazed surfaces comprises a significant part of a building's total energy loss, and can typically approximate 50% of the total loss. These losses occur during the heating season as a consequence of a low insulating rating and outward heat flow, mitigated by the solar gain of any windows and walls exposed to the sun. During the cooling season, inward solar heat flow detracts from the insulating characteristic of the building walls and windows, unless shading is employed.
Attempts to improve the thermal transfer properties of glazed surfaces and particularly to decrease heat loss through glazed surfaces have in the past primarily consisted of shutters over the outer surface, for example, wooden “doors” from colonial times to modern motor-driven roll-up “slats”. External covers suffer from an intrinsic R-value limitation on the order of 5 hrft2F/BTU per inch of thickness. The consequent rather bulky cover further precludes the application of such covers to curtain-wall structures, such as large buildings. It is also difficult to construct such covers to be weather tight, movable, and reliable.
Alternatively, curtains, shades, Venetian blinds, Roman shades, drapes and other interior window covers have been used to control thermal transmissions through windows. The effectiveness of internal covers is limited by a combination of factors including high infrared emissivity, air convection within the room spaces and leakage of air around and through window and wall surfaces.
A number of patents have issued that teach attempts to decrease air convection via improved sealing around the periphery of the frame of the window. All of these methods attempt to control heat and light flow by converting a “window” into a “wall”. None of them, however, have produced structures yielding R-values approaching that of a frame wall. Some of these patents propose the use of metallized films or fabrics to decrease infrared emissivity to perhaps 0.3, but the structures suffer from problems of dust build-up and the necessity to frequently clean the surfaces and consequent vulnerability to damage.
A third approach to reducing energy losses through windows has been to use multiple glazing layers and/or to increase the spacing between the layers to perhaps 3 to 4-inches. In one such arrangement, reference U.S. Pat. No. 3,903,665, dry, insulation particles (e.g. foam beads or particles of other insulation materials) are moved through provided air passages via a vacuum or gravity between a storage space and the glazing air space. While this “beadwall” approach has provided windows having reported R-values of the order of 20, several limitations exist. That is, the ducts or passages to and from these windows must be incorporated in the adjoining building structure or window framing. The beads occupy significant storage space when the windows are emptied. The glazing surfaces in contact with the beads tend to become covered with dust and statically suspended particles over time. The static electric charges can also rise to the point where high voltage discharges can result.
Yet another approach to attaining energy efficiency has been to use multiple layers of shading. For example, U.S. Pat. No. 4,187,896 shows a semitransparent curtain layer having a lowered infrared emissivity on an outer surface. The layer is suspended within the room space in the fashion of a shade and is mounted to a roller assembly. U.S. Pat. No. 4,039,019 describes the use of three or more mutually parallel, opaque shades. The shades can be attached to a retracting device and cover an internal building opening, such as a window. A number of resilient spacers separate the adjacent sheets and create several dead air spaces.
A variety of motor drives for shades are also found at U.S. Pat. No. 6,201,34, which discloses a digital microprocessor control with Hall Effect sensors used to sense limits. U.S. Pat. No. 6,082,443 uses a PLC to “learn” position limits for a motor equipped with a revolution counter. And U.S. Pat. No. 6,060,852 discloses a DC motor and battery mounted in a hollow tube.
The present invention improves upon the known art by providing a window assembly that provides a framework with two glazing layers and several intermediate planar films. The framework and films are arranged to obtain windows having R-values approaching that of framed walls. The films can also be raised and lowered via associated electro-mechanical assemblies to control relative ambient thermal conditions.